The Sciences

Revealing the Invisible Universe

Radio astronomy reveals celestial wonders hidden from the human eye.

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Photo Credits: National Astronomy and Ionosphere Center – Arecibo Observatory

The Arecibo Observatory in Puerto Rico is one of the world’s most recognizable radio telescopes, thanks to cameos in movies such as “Contact” and the James Bond film Goldeneye. Constructed in 1963 by the Department of Defense to study the Earth’s ionosphere—the atmospheric layer ionized by solar and cosmic radiation—the 305-meter dish sits in a naturally formed limestone sinkhole. In 1969, NSF took over operations and converted Arecibo into a national research center.

The observatory’s long history is punctuated with discoveries, from the detection of millisecond pulsars—neutron stars that rotate several hundred times a second—to the presence of hydrocarbon lakes on Saturn’s moon Titan.

Photo Credits: NRAO/AUI/NSF; D. Berry/Skyworks

An artist’s impression of a supermassive black hole at the center of NGC 1068, a barred spiral galaxy 47 million light years from Earth.

Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) to observe NGC 1068 discovered clouds of gas and dust being expelled from the black hole’s accretion disk, where dense material spins furiously around a black hole, sometimes reaching speeds of 400 to 800 kilometers per second. Eventually the black hole pulls material from the accretion disk into it, raising temperatures which emits a glow. While some material is pulled into the body, however, other material is expelled and, in some cases, forms a doughnut-shaped cloud of gas and dust, called a torus, around the entire system, concealing it.

Photo Credits: B. Campbell, Smithsonian, et al., NRAO/AUI/NSF, Arecibo

In 2012, astronomers combined radar data from the Arecibo Observatory and Green Bank Telescope to create this remarkably detailed image of Venus’ surface, which is hidden from direct view by a thick layer of clouds consisting mostly of sulfuric acid and carbon dioxide.

To see what lay beneath the Venusian clouds, astronomers at Arecibo sent radar signals to Venus. The signals passed through the atmospheres of both Earth and Venus, hit upon Venus’ surface and bounced back to the Green Bank Telescope. This transmitter-receiver technique revealed a planet characterized by mountains, ridges, craters and other surface features.

Photo Credits: B. Kent, A. Angelich, NRAO/AUI/NSF

Astronomers used the Very Long Baseline Array (VLBA) and NASA’s Cassini spacecraft to map the position of Saturn and her moons (seen here in this artist’s conception) to within about a mile. Using signals collected from Cassini’s radio transmitter, VLBA pinpointed the position of the spacecraft as it orbited. Combined with other data, VLBA provided a more accurate position of Saturn and its moons, which were 50-100 times more precise than those provided by ground-based optical telescopes.

NSF’s network of ground-based radio observatories, together with its optical/infrared, particle and gravitational wave observatories, advances the understanding of the universe and our place in it by continuing to reveal its hidden and visible wonders. The images in this NSF gallery are copyrighted and may be used only for personal, educational and nonprofit/non-commercial purposes. Credits must be provided.

Photo Credits: NRAO/AUI

This radio antenna in Owens Valley, California, is part of a continent-wide system of 10 telescopes—called the Very Long Baseline Array (VLBA)—funded by NSF and stretching from Hawaii to the Virgin Islands. Put together, VLBA antennas produce images hundreds of times more detailed than optical telescopes. The array is the world’s largest, full-time astronomical instrument.

Astronomers from around the world use VLBA to perform a number of astronomical feats, from mapping the universe with extreme precision to measuring tectonic motions and monitoring the rotation of the Earth, which is critical for ensuring accuracy with GPS systems.

Photo Credits: NRAO/AUI/NSF

With the help of radio telescopes like the Karl G. Jansky Very Large Array (VLA), astronomers can peer through the layers of gas and dust that saturate the Milky Way galaxy to study the supermassive black hole radiating at its core.

This image of the center of the Milky Way was created from multiple VLA observations. The circular rings in the center-left of the image are supernova remnants caught in the strong magnetic field of the galaxy’s core.

With the help of supercomputers that process large amounts of spectral data—a first for radio astronomy—the VLA is able to produce images of cosmic objects and events.

Photo Credits: Andrew Clegg, NSF

Though many cosmic phenomena are visible to us, much of the universe is hidden from view, obscured by gas and dust. After the serendipitous discovery of radio waves coming from the Milky Way’s center in the 1930s, scientists realized radio waves, which have a longer wavelength than visible light, could reveal many aspects of cosmic phenomena not visible in other wavelengths.

For more than 60 years, the National Science Foundation (NSF) has invested in state-of-the-art facilities to advance the field of radio astronomy, starting with the nation’s first astronomical observatory—the National Radio Astronomy Observatory (NRAO). Today, NSF supports radio telescopes from West Virginia to the Chilean Andes.

The following images offer a virtual tour of some of those telescopes and their discoveries.

Pictured: The Karl G. Jansky Very Large Array in New Mexico.

Photo Credits: NRAO/AUI/NSF

The Green Bank Telescope (GBT) in West Virginia is the world’s largest, fully steerable radio telescope. Nestled in a valley in the Appalachian Mountains, the Green Bank site is naturally shielded from most of the noisy radio signals that flood urban areas. It further operates within a 13,000-square-mile National Radio Quiet Zone, where fixed transmitters such as cellphone and radio towers are strictly regulated.

Radio waves from cosmic sources are much fainter than noisier radio waves closer to home. Hence, radio telescopes are typically located in more remote areas to minimize the homegrown noise.

Photo Credits: NRAO/AUI/NSF; Carlos Padilla 

The Atacama Large Millimeter/submillimeter Array (ALMA) is located in the Chilean Andes atop the Chajnantor Plateau. At an altitude of 16,500 feet, ALMA is one of the highest astronomical observatories on Earth.

ALMA’s array of 66 high-precision antennas act as a single telescope. Its sensitivity and high resolution—10 times sharper than the Hubble Space Telescope—are ideal for observing the “cool” universe, or the regions of gas and dust around stars. In this way, observations by ALMA and other radio telescopes complement those of optical telescopes.

Photo Credits: S. Schnee, et al.; B. Saxton, B. Kent (NRAO/AUI/NSF)

Captured by the Green Bank Telescope, these filaments of dust and gas (in orange) are brimming with pebble-sized particles that shine brightly in millimeter-wavelength light. The filament is located in the Orion Molecular Cloud Complex, a star-forming region that is home to the Orion Nebula.

Astronomers often observe microscopic dust grains—which can coalesce to form rocky planets—around protostars, or very young stars gathering mass from their parent molecular cloud. However, the interstellar particles found in this filament were 100 to 1,000 times larger than particles typically found in star-forming regions, leading astronomers to theorize the larger-than-expected particles could help spur planet formation.

The optical component of this image is made possible by NASA’s SkyView Facility at NASA Goddard Space Flight Center.

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